油井井下防腐工具的应用评价

Evaluation on Application of Corrosion Protection Downhole Tool in Oil-wells

目的 评价井下防腐工具的现场应用效果,探讨其对管杆的防腐应用前景。方法 通过对延长油田某区块油井采出水进行水质分析,并结合室内腐蚀试验,测定油井管材在该采出水中的腐蚀速率。选取腐蚀严重的油井安装井下防腐工具,定期检测安装工具后产出液中总铁离子的含量和管材的腐蚀速率。对比安装前后的修井次数、油管和抽油杆的更换数量、总铁离子的含量、腐蚀速率,综合评价井下防腐工具的应用效果。结果 实施措施前,管材的腐蚀速率在0.199～0.386 mm/a之间,远远超出了0.076 mm/a的标准要求。实施措施后,每口井每年平均修井次数由3.4次下降到1.2次,下降率为64.7%;每口井的油管和抽油杆每年平均更换长度由11.6、33.6 m分别下降至5.7、8.0 m;总铁离子含量的下降率都在42%以上。结论 该区块采出水中的腐蚀性介质（溶解氧、CO2、H2S、Cl^-）含量较高,对油井管材造成了严重腐蚀。安装井下防腐工具后,管杆的更换数量、产出液总铁离子含量及腐蚀速率均大幅下降,表明该工具能有效减缓井下管柱的腐蚀,具有一定的现场应用前景。

Objective To evaluate the field application of corrosion downhole tool and explore the prospects for corrosion protection of tube rod. Methods Quality of water produced in oil-well of a block of Yanchang Oil Field was analyzed; and then corrosion rate of oil-well tubes in the water was determined by combining with indoor anticorrosion test. Corrosion protection downhole tool was installed in selected severely corrosive oil-wells. Content of total iron ion in the output liquid and corrosion rate of tubes after the tool was installed were regularly detected. Workover frequency, number of replaced tubes and sucker rods, content of total iron ion and corrosion rate were compared before and after installation so as to evaluate the application effect of corrosion protection downhole tool. Results Before the application, corrosion rate of tubes was 0.199-0.386 mm/a, far higher than the required 0.076 mm/a. After the application, workover frequency decreased from an average of 3.4 times per year to 1.2 times per year, down 64.7%; the average replacement length of tube and sucker rod in each well decreased respectively from 11.6 m/a and 33.6 m/a to 5.7 m/a and 8.0 m/a; total iron ion content decreased by over 42%; Conclusion Corrosive media in the block produced water （oxygen, CO2, H2S, Cl^-） are higher and severely corrode oil pipes and tubes. After installation of corrosion protection downhole tool, number of replaced sucker rods, content of total iron ion in output liquid output and corrosion rate all decline significantly. That indicates the tool can effectively slow down the corrosion of downhole string and enjoys application prospect to some extent.